"The M17 Project" by Ira Brodsky, KC9TC

Py ~
OPN
“5 ATX#A,
a) Sees oO

FIGURE 1: OpenHT, an open-source SDR-based handheld transceiver.

his is an open-source digital voice standard which
promotes innovation, and which should attract
young ‘hardware hackers’ to amateur radio.

Introducti

4

e)

n

The freedom to design, build, and experiment has always been an important
part of amateur radio. As our hobby migrates to digital voice technology, that
freedom may be limited by proprietary technology used to code and decode
the signals. What experimenters need is an open-source digital standard, ie a
standard that anyone can use without having to buy a licence or pay royalties,
and that anyone can extend or modify provided that they share their code with
the amateur-radio community.

Digital voice (DV) in the UK’s VHF and UHF bands is currently served by
no fewer than seven different standards: System Fusion from Yaesu (YSF),
digital mobile radio (DMR) from the European Telecommunications Standards
Institute (ETSI), D-STAR from Icom, next-generation digital narrowband
NXDN) from Icom and Kenwood, project 25 (APCO P25) developed by
public safety professionals in North America, terrestrial trunked radio (TETRA)
developed by public safety and two-way radio industry experts together with
ETSI, and M17 developed by a community of open-source developers and
radio enthusiasts. Four of these standards use the proprietary advanced
multi-band excitation (AMBE+2) codec (a codec is a device that converts
analogue voice signals to digital signals for transmission, and digital signals
to analogue voice signals on reception), designed and licensed by Digital
Voice Systems Inc (DVSI). D-STAR and TETRA use older codecs: D-STAR uses
AMBE and TETRA uses algebraic code-excited linear prediction (ACELP) that,

—

NJ spswwp CANO
x4 ig LAST

Menu
S [Revision f
opm. 5 oa 1.3inch OLED Module (C ‘
, $ ; . . ‘ .

FIGURE 2: The Module 17 modem.

while beyond its 20-year patent protection period, still contains proprietary
elements. M17 uses the completely-free and open-source codec 2, developed
specifically for amateur radio. A comparison between the various standards
is shown in Table 1.

It’s important to keep all roads to innovation open. Amateur radio operators
have made significant contributions to the technology over the years. For
instance, Louis Varney, GORV invented his popular multiband antenna, and
Edwin H. Armstrong, W2MXN invented FM radio.

Amateur radio enthusiasts, who hope to make contributions to digital
voice technology, may encounter obstacles. When equipment manufacturers
decided to offer digital voice, they had two options. They could develop codecs
for amateur radio from scratch, not a trivial task, or they could license codecs
already developed for commercial and public-safety markets. For reasons
that made good business sense at the time, they decided to license existing
technology. However, this created a couple of problems for home-brewers and
experimenters. It meant that anyone making their own interoperable device
would have to purchase a codec from a licensed manufacturer. That may not
sound like a big imposition, but it limits the home-brewer’s design choices.
And anyone wanting to customise a commercially-manufactured radio might
be prevented from doing so if the codec is implemented in firmware. The
manufacturer might not care if it’s just one radio, but what if that person
decides to share their code by publishing it online?

There is another argument for developing codecs specifically for amateur
radio. Although the licensed codecs are the result of years of development and
experience in commercial and public-safety markets, they aren’t optimised for
amateur radio applications, which are exceptionally diverse and continue to
evolve. Free and open-source codecs would give the amateur radio community
greater control over its future.

May 2024

M17 is a reasonable solution, both in terms of
ensuring experimenters are free to experiment, and
providing a way forward. The M17 specification,
source code, hardware designs, and algorithms
are all open. The software is licensed under the
GNU general public licence version 2.0, and the
hardware under the Tucson amateur packet radio
(TAPR) open hardware licence. There is also a
management system to facilitate sharing of source-
code additions and changes.

There is one more problem that M17 might
be able solve. Because there are several different
standards, radios can only talk to repeaters and
other radios supporting the same standard. The
market for VHF/UHF amateur radios is, therefore,
quite fragmented. An open-source standard could
serve aS a vendor-neutral bridge between the
standards, by enabling dual-mode mobile radios,
handheld transceivers, hotspots, and repeaters
(M17-YSF, M17-DMR, etc). This would promote
greater interoperability, and would facilitate the
long-term development of a universal digital voice
standard for amateur radio, all while continuing to
protect the manufacturers’ investments in current
standards.

Enter the M17 project

The M17 project was founded by Polish
radio amateur Wojciech Kaczmarski,
SP5WWP in 2019. The name ‘M17’ comes
from the street address of a radio club in
Warsaw (Mokotowska 17). After obtaining
his licence in 2016, Kaczmarski began
experimenting with Codec 2, the open-source
codec developed by David Rowe, VK5DGR
for FreeDV, some software for using digital
voice in the HF bands. Kaczmarski wanted
to create an alternative to the popular DMR
standard, because the DMR specification is
difficult to understand, and its proprietary
codec inhibits ‘hacking’, a term many people
use for building and modifying hardware.
The effort attracted support, the project grew,
and in 2021 Kaczmarski received the ARRL
Technical Innovation Award for developing
the M17 protocol.

The goal of the M17 project is to ensure that
the amateur radio community has the freedom
to build, learn, and innovate by creating and
evolving a digital voice/data protocol specifically
for amateur radio. M17 supporters believe that it
will lead to more interesting products and that, in
turn, will make amateur radio more attractive to
young people.

Enthusiasm for designing, tinkering, and
inventing is very much alive in the amateur-
radio community. Recent examples include:
multi-mode digital voice modem for hotspots and
repeaters (MMDVM), high-performance software-
defined radio (HPSDR), experimental firmware
for select radios (OpenRTX), and multi-platform
software for digital modes like PSK31 (Fidigi) and
FT8 (WSJT-X). The M17 Project is driving the
development of OpenHT, an open-source SDR-
based handheld transceiver that operates in the

ay 2024

Hosts About

Disconnect

Mic 50.0
SrclD
DstID
Type
Frame#

StreamID

AMBE: No device
MMDVM: No device

Connected ping cnt: 3

FIGURE 3: Droidstar digital voice client software.

440MHz and 2.4GHz bands, and that supports
a variety of modulation schemes (including AM,
FM, SSB, 4FSK, and SSTV). OpenHT will enable
amateur radio enthusiasts to build and customise
small handheld transceivers (see Figure 1).

Though proprietary technology has its place
(for example the Apple computer), independent
developers and experimenters tend to prefer open
systems. Open systems drew many people to
TCP/IP and Linux. TCP/IP triumphed because it
was just good enough, easy to implement, and
not proprietary. Linux provided an alternative to
operating systems controlled by large corporations
such as Microsoft and Apple.

M17 is already attracting young people; most
M17 hackers are in their 20s or 30s. The M17
specification is relatively easy to understand, and
can even be used as a digital communication
teaching tool. M17 has also attracted financial
grants: Amateur Radio Digital Communications
(ARDC), a private foundation supporting amateur
radio technology development, awarded the M17
Project $250,000 in 2021 and an additional
$228,900 in 2022.

The M17 specification

The M17 specification can be viewed and
downloaded at [1]. The specification defines three
network layers: the physical layer, the data-link

ayer, and the application layer. The M17 protocol
is versatile, supporting voice, point-to-point data,
and telemetry. The M17 specification is also
extensible so new capabilities may be added over
ime.

The physical layer describes the air interface:
how ones and Zeroes are represented over the air
using 4-level frequency-shift keying (4FSK), the
number of bits per symbol (2), and the symbol
rate (4,800 symbols per second times 2 bits per
symbol = 9,600 bits per second). M17 uses
channels of width 9kHz with 12.5kHz spacing.
Each transmission includes a preamble (to
prepare the receiver), a synchronisation burst (to
align the clock), the data payload, and an end-of-
transmission marker.

The data-link layer describes how the data
is organised into the four types of frames (link
setup, bit error rate test, stream mode, and packet
mode), and the error correction method. The link
setup frames include the source and destination
addresses. The bit error rate test frames are used to
est hardware, and ensure interoperability between
disparate devices. The stream frames are used to
send continuous data such as voice. The packet
rames are used to send data in packets of up to
823 bytes each. The throughput ranges from 3kbps
0 4.7kbps, depending upon the packet size.

The application layer describes how various
asks are accomplished. For instance, it defines
parameters for audio streaming using Codec 2, and
he protocol (such as automatic packet reporting
system (APRS), AX.25, etc) when transmitting
packet data. Codec 2 offers good audio quality at
ow bit rates (1,600 or 3,200 bps). The application
ayer also defines parameters specific to user
devices (clients), repeaters, and gateways (such as
internet reflectors). M17 is designed to support IP
networking for repeater linking and communicating
via internet reflectors. M17 also supports strong
encryption for use where legal (eg in Poland).

M17 development projects

There are currently several efforts underway to
develop M17-capable hardware, as well as to
adapt M17 to existing hardware. Repositories of
software code for many of the following projects
can be found at Github (see [2]). M17 community
participants can also be found chatting on Discord
[3].

Module 17 [4] is a modem that sits between
the microphone and radios capable of running
9600bps, such as the Kenwood V71 and D710,
and the Motorola CDM series. Module 17’s
baseband output feeds into the radio's packet data
input. See Figure 2.

The popular Digirig computer interface [5]
can now be used to run M17 from a PC, using
software and a soundcard, with radios such as the

Ira Brodsky, KC9TC

ibrodsky64@gmail.com

#1

Yaesu FTM-200, FTM-300, FTM-400, and FTM-
500. The Digirig cable is connected to the packet-
data input and packet-data output pins.
Mobilinkd’s TNC4 [6] is a hardware-based
solution for adding M17 to a radio. It is an open-
source TNC platform, and is also available in a
bread-board configuration (NucleoTNC). The
TNC4 and NucleoTNC provide alternatives to the
PC-plus-soundcard approach.
The OpenRTX project [7] develops free and
open-source firmware for digital amateur radio.
The goal is to enable amateur radio operators
and experimenters to customise and add features
(such as voice prompts, different languages, and
M17 support) to existing radios. Note that this
project is being pursued independently of the
manufacturers; changing the radio’s firmware is
carried out at the owner’s risk, although users are
encouraged to keep a backup copy of the factory
firmware, which in most cases is easy to reinstall.
OpenRTX could enable upgrading a DMR radio
to a dual-mode DMR/M17 radio (assuming that
there are no legal obstacles). Radios used in the
OpenRTX project currently include Tytera MD-
380/390, MD-UV380/390, and TYT MD-9600,
Radioddity GD-77, and Baofeng DM-1801.
Multi-mode digital voice modem (MMDVM)
[8] is an open-source hardware/software modem,
developed by Jonathan Naylor, G4KLX that
supports all amateur-radio digital voice standards,
including M17. It is widely used in hotspots and
repeaters. It runs on platforms that use ARM
Cortex-M3, M4, or M7 processors, such as the
Arduino Due. MMDVM_HS is José Andrés Uribe’s
(Andy, CA6JAU) hotspot version. MMDVM_CM is
Doug McLain’s, AD8DP solution for adding cross-
mode capability to internet reflectors (eg M17 to

YSF). M17Client, also by Jonathan Naylor, adds
M17 to MMDVM modems and hotspots, and
includes features such as voice, simultaneous text
messaging, and GPS locating data.
WPSD [9] is a digital voice management
suite of software for hotspots and repeaters that
supports M17, DMR, D-Star, YSF, P25, and
NXDN, and runs on the Raspberry Pi. The name
is an acronym for ‘WOCHP-PiStar-Dash’, and is
derived from the author’s popular Pi-Star software.
WPSD works with MMDVM, but doesn’t do any
encoding or decoding; it just takes data from the
radio-modem combination and sends them over
the network, and takes data from the network and
sends them back to the radio via the modem.
Mvoice software [10] runs on Linux and
can be used to transmit and receive M17 over
the internet. A user with just a headset and a
Raspberry Pi (or other Linux device) can use it to
connect to an M17 reflector, and chat with other
M17 users.

Mrefd [11] is an M17 reflector program that
supports up to 26 channels. M17 clients (such
as devices running Mvoice), M17 hotspots,
M17 repeaters, and other M17 reflectors can be
linked to each channel. The voice stream from
each client is heard by all other clients on that
channel. Mrefd runs on Linux (Debian or Ubuntu
distribution recommended).

DroidStar [12] is digital voice client software
that runs on multiple platforms (including Android,
iOS, Linux, Windows, and MacOS) and supports
multiple digital voice protocols (see Figure 3). It
comes with M17 built-in; additional protocols
require a plug-in voice encoder (vocoder).
Droidstar can be used to talk directly over the
internet or a radio and a modem can be added to

»

turn a mobile phone into a hand-held transceiver.

M17 is also being integrated with software
defined radio platforms. SDR++ software for
Windows, MacOS, and Linux [13] includes a
built-in M17 decoder. OpenWebRx, a web-based
multi-user receiver [14] that can be operated from
any web browser, will also support M17.

M17 and the future of amateur radio

In an increasingly digital and internet-
connected world, it’s essential that radio
amateurs continue to develop their digital
voice/data capabilities. An open-source
standard is needed so that the entire amateur
radio community, licensed operators as well
as equipment manufacturers, can contribute
to the process. M17 appears to be well-
positioned to help make that happen.

References

https://spec.m17project.org
https://github.com/M1 7-Project
https://discord.gg/G8zG phypfé
https://github.com/M17-Project/Module_17
https://digirig.net/
h
h
h

=

ttps://store.mobilinkd.com/products/mobilinkd-tnc4
ttos://openrtx.org/#/
ttos://github.com/g4klx/M
https://wOchp.radio/wpsd/
0] https://github.com/n7tae/mvoice

] https://github.com/n7tae/mrefd

12] https://github.com/nostar/DroidStar

13] https://github.com/AlexandreRouma/SDRPlusPlus
14] https://www.openwebrx.de/

DVM

1
2
3
4
5
6
7
8
9
1

=

Table 1: M17 compared with the other VHF/UHF digital voice standards used by radio amateurs in the UK.

M17 System Fusion DMR D-STAR NXDN APCO P25 TETRA
Approx. number
of Repeaters, UK 9 373 318 209 By 53 i
Developer/Vendors Amateur radio Yaesu/Yaesu European Telecomms = Japan Amateur Icom and Association of Public © European Telecomms
community/ Standards Institute’ Radio League/ Icom, Kenwood/ Safety Comms Standards Institute/
multivendor multivendor Kenwood, and Flex = multivendor _—Officials/ multivendor multivendor
Type of standard Free and open Proprietary Partially open Partially open Partially open Partially open Partially open
source
Codec Codec 2 (open AMBE+2 AMBE+2 AMBE (copyright- AMBE+2 AMBE+2 (patent- ACELP
source) (patent-protected) — (patent-protected) protected) (patent-protected) protected) (codebook-protected)
Modulation AFSK 4FSK AFSK GMSK 4FSK AFSK DQPSK
Data features Callsign, text Callsign, text Callsign, text Callsign, text Callsign, text Callsign, text Callsign, text messages,
messages, location, messages, messages, location messages, location, essages, messages, location location
images location, images images location
Advantages Fully open source, Largest installed Well supported, Created for amateur Can use 12.5 Designed for Supports four
created for amateur base of repeaters, talkgroups radio, up to 128 or 6.25 kHz emergency simultaneous
radio WIRES-X kbps data channels communication conversations in 25 kHz
Disadvantages Limited installed Single vendor Designed for Inferior codec, Designed for Mainly used gear for Equipment for
base (new entrant) ; commercial use, expensive commercial amateur use, not all amateur use
difficult to set codeplug & public safety, models suitable for limited to
limited installed amateur radio 430 MHz band
base

y

May 2024